Early-Middle Pleistocene Boundary Research Articles

The stratigraphic transition and suggested boundary between the Early and Middle Pleistocene in the loess record of northern Eurasia

Abstract This review focuses on the loess-palaeosol record across the Early-Middle Pleistocene transition to show the main structural features in key sections from the Loess Plateau of China via central Asia to Europe. Loess-palaeosol sequences in general demonstrate an impressive coherence with oxygen isotope osillations, providing a high-resolution terrestrial record for stratigraphic subdivision. Accordingly, they are considered useful for detailed climatostratigraphy and correlation. Nonetheless, there are many uncertainties in loess-palaeosol stratigraphic correlation across the Early-Middle Pleistocene transition from region to region within northern Eurasia. The interval between the top of the Jaramillo Subchron and the Matuyama-Brunhes (M-B) Chron boundary is discussed in detail because it embraces suitable horizons for placing the Early-Middle Pleistocene boundary. This interval contains a variable number of loess and palaeosol horizons in sections along the different loess provinces from east to west. A distinctive palaeosol unit just below the M-B reversal can serve as a marker horizon for establishing the Early-Middle Pleistocene boundary. In south Tajikistan, it corresponds to the pedocomplex 10 (PC10) and to palaeosol S8 in the Loess Plateau of China. The base of this soil horizon correlated with the base of Marine Isotope Stage 21 can be considered as a distinctive geological level for recognizing the Early-Middle Pleistocene boundary on the continent.

Long-term river terrace sequences: Evidence for global increases in surface uplift rates in the Late Pliocene and early Middle Pleistocene caused by flow in the lower continental crust induced by surface processes

AbstractLong-term river terrace sequences reveal that many regions have uplifted by several hundred metres since the Middle Pliocene. They indeed provide evidence of a global increase in uplift rates in die Late Pliocene, followed by a calm period then a renewed increase around the Early-Middle Pleistocene boundary. It is suggested that this uplift pattern has resulted from thickening of the continental crust caused by flow in the lower crust which has been induced by cyclic surface loading caused by growth and decay of ice sheets and the associated global sea-level fluctuations. Observed uplift histories are modelled using a technique which incorporates increases in the strength of forcing of this process caused by step changes in the intensity of glaciations starting at~3.1,~2.5,~1.2, and~0.9 Ma.

Diatom Biostratigraphy of the Kazusa Group, Boso Peninsula, Honshu, Japan.

Since the Kazusa Group is considered as the candidate to stratotype of the Early-Middle Pleistocene boundary in the Pacific region, it is urgent to investigate the Kokumoto Formation as a member formation of the Kazusa Group. The paleomagnetic boundary between C1r (Matuyama) and C1n (Brunhes) is recognized at the ash marker bed “Shirao” in the middle part of the Kokumoto Formation. The diatoms from the Otadai, Umegase, Kokumoto, Kakinokidai, and Chonan Formations along the Yoro River, in the middle part of the Boso Peninsula, about 80km southeast of Tokyo, have been studied. The marine sequences are dominated by shelf-water Paralia sulcata (Ehrenberg) Kützing indicating shallow water sedimentation. The seven diatom datum levels (biohorizons) allow precise correlation in the transitional region of the northwest Pacific Ocean. Among them the four biohorizons appear synchronous near the Early-Middle Pleistocene boundary in the Kokumoto Formation: LO (last occurrence) of Actinocyclus oculatus Jousé and LO of Rhizosolenia matuyamai Burckle at the lower part of the boundary, and LO of Nitzschia fossilis (Frenguelli) Kanaya and LO of Nitzschia reinholdii Kanaya at the upper part of the boundary. The regressions were recognized twice at the basal part of C1r. 1n (Jaramillo) in the Otadai Formation and across the C1r and C1n (Early-Middle Pleistocene boundary) in the Kokumoto Formation. The Kokumoto Formation is suitable as the candidate to stratotype of the Lower-Middle Pleistocene boundary of the Pacific region based on diatom biostratigraphy.

Calibration of the Early-Middle Pleistocene transition in the continental beds of the Guadix–Baza Basin (SE Spain)

The magnetostratigraphic and palaeontologic studies carried out in two sections in the Guadix–Baza Basin (SE Spain) have enabled an accurate calibration of the Early-Middle Pleistocene boundary in the continental beds of this basin. The palaeontological record (rodents) in the Cortes de Baza section indicates an age ranging from the earliest Pleistocene (latest Villanyian or early Biharian) to the late Early Pleistocene (late Biharian). The whole Cortes de Baza Section is placed in a reversed magnetic interval identified as the upper part of the Matuyama Chron. In the Guadix–Baza Basin, the Middle Pleistocene (early Toringian) was already known at the locality of Cúllar–Baza I, but new studies in the area have resulted in the recognition of Early Pleistocene deposits in the lower part of the section. Thus, the locality of Cúllar–Baza B is placed in a reversed magnetozone correlated with the uppermost Matuyama, while the locality of Cúllar–Baza C is placed in a normal magnetozone correlated to the lower Bruhnes Epoch. Therefore, the Biharian–Toringian boundary (based on the presence of Arvicola cantiana) falls well within the Bruhnes epoch. This result is consistent with what is found in other Early–Middle Pleistocene sections of Spain (Atapuerca Gran Dolina).